The current understanding of the crystallization, morphology evolution, and phase stability of wide‐bandgap hybrid perovskite thin films is very limited, as much of the community's focus is on lower bandgap systems. Herein, the crystallization behavior and film formation of a wide and tunable bandgap MAPbBr3
The proposed X-ray spatial light modulator (SLM) concept is based on the difference of X-ray scattering from amorphous and crystalline regions of phase change materials (PCMs) such as Ge2Sb2Te5(GST). In our X-ray SLM design, the
- NSF-PAR ID:
- 10369414
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 12
- Issue:
- 4
- ISSN:
- 2159-3930
- Format(s):
- Medium: X Size: Article No. 1408
- Size(s):
- Article No. 1408
- Sponsoring Org:
- National Science Foundation
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− x Clx system are investigated, and its formation and phase stability are contrasted to the classical MAPbI3− x Brx case. A multiprobe in situ characterization approach consisting of synchrotron‐based grazing incidence wide‐angle X‐ray scattering and laboratory‐based time‐resolved UV–Vis absorbance measurements is utilized to show that all wide‐bandgap perovskite compositions of MAPbBr3− x Clx studied (0 <x < 3) crystallize the same way: the perovskite phase forms directly from the colloidal sol state and forms a solid film in the cubic structure. This results in significantly improved alloying and phase stability of these compounds compared with MAPbI3− x Brx systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to methylammonium lead iodide (MAPbI3). The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin‐hole‐free MAPbBr3− x Clx hybrid perovskite thin films with a tunable bandgap are, thus, integrated into working single‐junction solar cell devices and achieve a tunable open‐circuit voltage as high as 1.6 V. -
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We calculate critical electronic conduction parameters of the amorphous phase of Ge 2 Sb 2 Te 5 (GST), a common material used in phase change memory. We estimate the room temperature bandgap of metastable amorphous GST to be E g (300K) = 1.84 eV based on a temperature dependent energy band model. We estimate the free carrier concentration at the melting temperature utilizing the latent heat of fusion to be 1.47 x 10 22 cm -3 . Using the thin film melt resistivity, we calculate the carrier mobility at melting point as 0.187 cm 2 /V-s. Assuming that metastable amorphous GST is a supercooled liquid with bipolar conduction, we compute the total carrier concentration as a function of temperature and estimate the room temperature free carrier concentration as p(300K) ≈ n(300K) = 1.69×10 17 cm -3 . Free electrons and holes are expected to recombine over time and the stable (drifted) amorphous GST is estimated to have p-type conduction with p(300K) ≈ 6×10 16 cm -3 .more » « less
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A magnetron co-sputtering system was used for producing nickel-doped Ge2Sb2Te5 (GST-Ni) thin films. The nickel content in the thin film was adjusted by the ratio of the plasma discharge power applied to the GST and nickel targets, as well as a physical shuttering technique to further control the nickel deposition rate. The doping concentration of the film was con firmed using Energy Dispersion Spectroscopy (EDS) technique. Results from a four-point probe measurement indicate that the nickel doping can reduce the resistivity of GST in the amorphous state by nearly three orders of magnitude. The dopant's influence on crystallization behavior was studied by analyzing X-Ray Diffraction (XRD) patterns of the pure GST and GST-Ni at different annealing temperatures. To examine the structural changes due to the nickel dopant, the thin films were investigated with the aid of Raman scattering. Additionally, we extracted the optical constants for both the amorphous and crystalline states of undoped-GST and GST-Ni films by ellipsometry. The results indicate that at low doping concentrations nickel does not appreciably affect the optical constants, but dramatically improves the electrical conductivity. Therefore, nickel-doping of GST a viable method for designing optical devices for lower operating voltages at higher switching speeds.more » « less
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